Not sure if this is the right place to ask this.

When I was looking at a die shot of the VRC7 chip, I saw these circuits on most of the input pins. I wanted to verify that I've understood the circuit correctly, since to me the configuration of transistors seem odd. The link also has a Visual6502 style coloration as well as a transistor circuit. The lower metal strip is input and the upper metal strip is output. The outputs always go to a gate of a transistor (except for /debug pin that has a power source on the output line to force the line high). The circuit most likely is a ESD/over-voltage protection circuit.

Do you think that the configuration I came up with is correct or not?

I'm not sure the fat poly on the right is actually a transistor: I don't see edges where the active crosses the poly. This structure isn't obvious to me - and nor is the whole assembly!

Are you sure the rail that you've coloured green is the ground rail?

Yeah I'm sure of that. I used a logic gate that I could clearly see to figure which rail was power and which ground and then just followed them and colored over them to map them out.



I too was questioning whether there actually is a transistor. Perhaps it was supposed to be something, but then it was disconnected? The pin should still work without it, even though it doesn't seem to have any protection (although I'm not sure if it even needs any).